Recent developments in medical device technology have led to the development of low cost devices for measuring physiological characteristics of a patient suffering from a chronic disease. As a result of these measurements marked improvements in treatment are possible because the type of treatment is responsive to the result of a measurement.
As an example, diabetes patients now measure blood sugar several times a day to determine when to administer insulin and how much insulin is required. Management of other chronic diseases could require monitoring multiple physiological measurement including pulse rate, blood pressure, respiration rate, body weight, spirometric parameters, etc.
Unfortunately, however, the possibilities of the improved technology often have not been realized because of patient inability to use the device, or understand the meaning of the device output. Often, effective treatment requires that measurements be taken over time and plotted on a graph to determine patient tendencies and the oncoming of a crisis. There are also problems on the health care provider side, with increased physician workload preventing the physician from monitoring compliance and gathering, formatting data, and interpreting data.
The following is a detailed discussion of the problems inherent in treating chronic asthma. Recent events suggest that there is an abundant need for data collection and reporting tools for use in the treatment of chronic asthma. The U.S. National Center for Health Statistics estimates that 12 million Americans--nearly 5% of the population--have asthma. Asthma morbidity and mortality rates increased dramatically during the 1980's. The reasons for these increases are not well understood. In the 1980's leading medical researchers began to view asthma as primarily an inflammatory response in the airways rather than bronchospasm. Consequently, they began advocating a new pharmacological therapy, anti-inflammatory medications. Furthermore, numerous studies of self management programs have documented the importance of early warning detection and patient-physician cooperative management in the long-term treatment of chronic asthma.
In August 1991 the National Asthma Education Program (NAEP), which was organized by the National Institutes of Health, published its Expert Panel Report: "Guidelines for the Diagnosis and Management of Asthma". In its foreword the Expert Panel Report states: "People with asthma can expect to control their symptoms, prevent asthma episodes, be physically active, and breathe normally. This report presents guidelines to help clinicians and patients meet these goals of asthma care." The report suggests regimens for pharmacological therapy, emphasizes the role of anti-inflammatory medication, and warns about the risks of over- and under-medication. The report stresses the importance of fostering a partnership among patient, family, and physician in the achievement of a successful self-management program for asthma sufferers.
Peak Flow Meters and Asthma Management
Peak flow meters have been around for a number of years. Many clinicians recognize that daily PEFR measurements can provide early warnings of an asthma attack. However, self-management programs which urge daily peak flow monitoring continue to be the exception rather than the rule. In advocating a preventative approach to asthma care, the National Asthma Education Program is urging clinicians and patients to adopt a preventative rather than an interventional approach to managing asthma.
The peak flow meter measures Peak Expiratory Flow (PEF), defined as the maximum rate at which an individual can expel air from the lungs, using maximal effort from full inhalation. PEF is measured in liters per minute. The highest value obtained in up to three attempts is recorded into a peak flow diary, which is usually a handwritten chart.
The personal spirometer typically measures several respiratory parameters, including the Forced Expiratory Volume (FEV.sub.1), defined as the volume of air expelled by an individual in the first second of exhalation, using maximal effort from full inhalation. FEV.sub.1 is measured in liters.
Physicians can gain several advantages by having access to accurate respiratory status data:
in evaluating the efficacy of the current medication regimen PA1 in detecting seasonal patterns, a rising or falling personal best, PEF and FEV.sub.1 trends PA1 in assessing airway stability over large blocks of time PA1 in assessing compliance with the self management program, including daily peak flow monitoring PA1 in providing a basis for an incentive system that physicians and/or parents can use to reward good compliance PA1 1. They are expensive because their designs are not inherently low cost. PA1 2. They fail to minimize the inconvenience of daily monitoring regimens by not creating a memory-resident longitudinal record which is immediately accessible via the device's human interface. PA1 3. They do not present any trend information by showing the results of preceding tests. PA1 4. They do not deliberately focus the user's attention on airway status and trend; their human interfaces are poorly suited for use by small children. PA1 5. They do not allow the user to label some test results as post medication results. PA1 6. They do not provide the user with a low cost mechanism to deliver the clinical information to the physician in a timely and efficient manner. PA1 7. They do not provide the physician with a crisp, graphical report designed to facilitate a sound, rapid interpretation and good medical treatment decisions. PA1 8. They fail to shield the physician from needing a computer to collect and review data. PA1 9. They do not address physicians' need to track compliance with the management plan nor a systematic method for reviewing the efficacy of the asthma management plan. PA1 10. They do not provide for the systematic collection of test results for statistical analysis.
According to the Expert Panel Report, PEF and FEV.sub.1 are useful in detecting the early signs of airway instability and in evaluating the efficacy of medication regimens. For instance, a patient can take PEF samples before and after administering a bronchodilator and thus have a basis upon which to evaluate the drug's efficacy in treating that patient's acute asthma episodes.
The Expert Panel Report is attempting to steer primary care physicians toward supporting patient self-management programs that entail daily peak flow monitoring. It recommends that patients 5 years or older with moderate or severe asthma measure their peak expiratory flow rates on a daily basis. Furthermore, it recommends that all patients and physicians employ peak flow meters and/or personal spirometers in their self asthma management programs.
The chairman of the NAEP's Expert Panel, Albert L. Sheffer, M.D., expressed his concerns about inadequacies in many home management programs for asthma: "All asthma patients who need daily therapy should be monitored with a peak flow meter. Meters are now used on fewer than 25% of those patients."
Guillermo R. Mendoza, M.D., a renowned expert in asthma diagnosis and treatment, made this statement: "Since 1978, despite a growing consensus about the value of peak flow monitoring, only a minority of primary care providers in the U.S. have adopted peak flow in their office practice. Few high risk asthma patients in this country have peak flow meters at home or know how to use them effectively."
A U.S. government publication makes this recommendation: "Ask your doctor about using a peak flow meter. A peak flow meter can tell you when an episode is coming--even before you feel symptoms. Taking medicine before you feel symptoms can stop the episode. People over age 4 with moderate or severe asthma should use a peak flow meter at least daily."
Prior Art: Mechanical Peak Flow Meters
In mechanical peak flow meters, the breath displaces a string-retarded deflector, which moves a pointer along a scale to indicate the test results. Most mechanical meters are simply pieces of molded plastic that have relatively poor inter-device accuracy and reproducibility. In their day these devices were useful to obtain fairly accurate readings, particularly where relative performance was more useful than absolute results. The creation of a longitudinal record depended solely on the discipline and care exercised by the user. Several examples of the mechanical type are listed below.
Prior Art: Electronic Peak Flow Meters and Spirometers
In the earliest models of electronic peak flow meters and personal spirometers, designers merely substituted a pneumotach sensor for the spring-retarded deflector in the mechanical device. All models use a microprocessor to handle the computations and a liquid crystal display to present the numerical test results.
Although current models of portable electronic spirometry devices offer more measurements and good reliability than mechanical peak flow meters, they offer little improvement to the practical challenge of maximizing the utility of home spirometry for both the user and the physician. Their many shortcomings are listed below.